Using Distance Spheres for Illustrating Stars, Black Holes, and the Speed of Light

Figure 1: Stars added to Sun Distance Spheres

Distance Spheres included in Starry Night allow “Cosmic Zoom” sequences in our domes. However, I also use them to show audiences scale sizes of stars, the Milky Way’s supermassive black hole, and the speed of light.

In a previous article I described the upcoming “Stellar Sizes” minilesson from the Fulldome Curriculum Volume 2. This program compares the sizes of a dozen different stars to each other on the dome. Here’s another captivating way to illustrate stellar scales, but this time compared to the size of the Solar System on the dome making use of Distance Spheres in Starry Night Dome.

I’ve added new Distance Spheres centered on the Sun and made them the appropriate scale according to the sizes of the stars as given in Starry Night and the scientific literature. The stars added as Distance Spheres are shown in Figure 1.

Figure 2: Betelgeuse compared to the Solar System

We can easily add a star’s size to its label name, so as they appear in the dome, their sizes will also show. I’ve colored them appropriately either by temperature or my prejudiced preference. It’s possible to change their opacities so that they look gaseous but you can also see planetary orbits through them, as shown in Figures 2 and 3 which show Betelgeuse and VY Canis Majoris (arguably the largest star known in the Milky Way).

I’ve also added the supermassive black hole that lurks at the center of the Milky Way, which is almost the same size as the star Arcturus. It’s very interesting to see how “small” this 4.3 million solar mass object is compared to the Solar System, as shown in Figure 4.

VY Canis Majoris compared to the Solar System

You can turn various spheres on and off in the dome via SciDome’s “QuickSphere” cue (QS) and or by loading various Starry Night files.

Another useful trick is hidden in a special Distance Sphere which is centered on the Earth, namely the time-varying Radio Sphere. The size of this sphere depends on the date you look at it as it’s expanding at the speed of light. The beginning point in time for this sphere is 12/12/1901 at 14:29:59 UT. So, I’ve set up a Starry Night simulation far enough away from the Earth to see the Moon’s orbit easily with the time stopped.

I tell my audience to watch carefully and they will see the light sphere expand away from the Earth in real time and reach the Moon’s orbit in 1.3 seconds, as seen in Figure 5.

Figure 4: Supermassive Black Hole of the Milky Way compared to the Solar System

You can also increase your elevation to encompass larger volumes of space to watch this sphere expand into the solar system. It’s educational to emphasize that, although light makes it to the Moon in slightly more than one second, it takes minutes to reach the planets, etc.!

I’ve found these to be great tricks for showing students the size of stars and our supermasive black hole compared to the size of our Solar System as well as illustrating the speed of light. I highly recommend that you play with this wonderful new tool in our SciDome teaching arsenal!

Figure 5: Light Sphere after traveling one second, almost to the Moon’s orbit

Dr. David H. Bradstreet is the primary author of the Spitz Fulldome Curriculum for SciDome planetarium systems. He is the Chair of Astronomy & Physics at Eastern University, as well as the Director of the University's Julia Fowler Planetarium and Bradstreet Observatory.